Discharge methodologies for lithium/silver vanadium oxide cells to manage voltage delay and permanent RDC growth region

ABSTRACT

It is known that reforming implantable defibrillator capacitors at least partially restores and preserves their charging efficiency. An industry-recognized standard is to reform implantable capacitors by pulse discharging the connected electrochemical cell about once every three months throughout the useful life of the medical device. A Li/SVO cell typically powers such devices. The present invention relates to methodologies for significantly minimizing, if not entirely eliminating, the occurrence of voltage delay and irreversible Rdc growth in the about 35 % to 70 % DOD region by subjecting Li/SVO cells to novel discharge regimes. At the same time, the connected capacitors in the cardiac defibrillator are reformed to maintain them at their rated breakdown voltages.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority based on provisional application Ser.No. 60/405,173, filed Aug. 22, 2002.

BACKGROUND OF INVENTION

1. Field of the Invention

The present invention generally relates to the conversion of chemicalenergy to electrical energy. More particularly, this invention relatesto an alkali metal electrochemical cell having reduced voltage delay andRdc growth. A preferred couple is a lithium/silver vanadium oxide(Li/SVO) cell. In such cells, it is desirable to reduce voltage delayand permanent or irreversible Rdc growth at about 35% to 70% ofdepth-of-discharge (DOD) where these phenomena typically occur.

2. Prior Art

Voltage delay is a phenomenon typically exhibited in a lithium/silvervanadium oxide cell that has been depleted of about 35% to 70% of itscapacity and is subjected to high current pulse discharge applications.The voltage response of a cell that does not exhibit voltage delayduring the application of a short duration pulse or pulse train hasdistinct features. First, the cell potential decreases throughout theapplication of the pulse until it reaches a minimum at the end of thepulse, and second, the minimum potential of the first pulse in a seriesof pulses is higher than the minimum potential of the last pulse.

On the other hand, the voltage response of a cell that exhibits voltagedelay during the application of a short duration pulse or during a pulsetrain can take one or both of two forms. One form is that the leadingedge potential of the first pulse is lower than the end edge potentialof the first pulse. In other words, the voltage of the cell at theinstant the first pulse is applied is lower than the voltage of the cellimmediately before the first pulse is removed. The second form ofvoltage delay is that the minimum potential of the first pulse is lowerthan the minimum potential of the last pulse when a series of pulseshave been applied.

Thus, decreased discharge voltages and the existence of voltage delayare undesirable characteristics of an alkali metal/silver vanadium oxidecell subjected to current pulse discharge conditions in terms of theirinfluence on devices such as implantable medical devices includingpacemakers and cardiac defibrillators. Depressed discharge voltages andvoltage delay are undesirable because they limit the effectiveness andeven the proper functioning of both the cell and the associatedelectrically powered device under current pulse discharge conditions.

Therefore, there is a need for a lithium/silver vanadium oxide cell thatis dischargeable to deliver the high capacity needed for poweringimplantable medical devices and the like, but that experiences little,if any, voltage delay and Rdc growth during pulse discharging,especially at about 35% to 70% DOD.

SUMMARY OF THE INVENTION

It is known that reforming implantable defibrillator capacitors at leastpartially restores and preserves their charging efficiency. Anindustry-recognized standard is to reform implantable capacitors bypulse discharging the connected electrochemical cell about once everythree months throughout the useful life of the medical device. Thus, thebasis for the present invention is driven by the desire to substantiallyreduce, if not completely eliminate, voltage delay and Rdc growth in aLi/SVO cell, while at the same time periodically reforming the connectedcapacitors to maintain them at their rated breakdown voltages.Methodologies for significantly minimizing, if not entirely eliminating,the occurrence of voltage delay and Rdc growth in the about 35% to 70%DOD region by subjecting Li/SVO cells to novel discharge regimes aredescribed.

These and other objects of the present invention will becomeincreasingly more apparent to those skilled in the art by reference tothe following description and to the appended drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph constructed from the average discharge results of twoLi/SVO cell groups, one pulse discharged under a 24 month ADD test at50° C., which is an accelerated test that simulates a 60 month ADD testat 37° C., the other accelerated pulse discharged according to amethodology of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The term percent of depth-of-discharge (DOD) is defined as the ratio ofdelivered capacity to theoretical capacity times 100.

The term “pulse” means a short burst of electrical current ofsignificantly greater amplitude than that of a pre-pulse currentimmediately prior to the pulse. A pulse train consists of at least onepulse of electrical current. If the pulse train consists of more thanone pulse, they are delivered in relatively short succession with orwithout open circuit rest between the pulses. An exemplary pulse trainmay consist of four 10-second pulses (23.2 mA/cm²) with about a 10 to 30second rest, preferably about 15 second rest, between each pulse. Atypically used range of current densities for cells powering implantablemedical devices is from about 15 mA/cm² to about 50 mA/cm², and morepreferably from about 18 mA/cm² to about 35 mA/cm². Typically, a 10second pulse is suitable for medical implantable applications. However,it could be significantly shorter or longer depending on the specificcell design and chemistry. Current densities are based on squarecentimeters of the cathode electrode.

An electrochemical cell that possesses sufficient energy density anddischarge capacity required to meet the vigorous requirements ofimplantable medical devices comprises an anode of a metal selected fromGroups IA, IIA and IIIB of the Periodic Table of the Elements. Suchanode active materials include lithium, sodium, potassium, etc., andtheir alloys and intermetallic compounds including, for example, Li—Si,Li—Al, Li—B and Li—Si—B alloys and intermetallic compounds. Thepreferred anode comprises lithium. An alternate anode comprises alithium alloy such as a lithium-aluminum alloy. The greater the amountsof aluminum present by weight in the alloy, however, the lower theenergy density of the cell.

The form of the anode may vary, but preferably the anode is a thin metalsheet or foil of the anode metal, pressed or rolled on a metallic anodecurrent collector, i.e., preferably comprising titanium, titanium alloyor nickel, to form an anode component. Copper, tungsten and tantalum arealso suitable materials for the anode current collector. In theexemplary cell of the present invention, the anode component has anextended tab or lead of the same material as the anode currentcollector, i.e., preferably nickel or titanium, integrally formedtherewith such as by welding and contacted by a weld to a cell case ofconductive metal in a case-negative electrical configuration.Alternatively, the anode may be formed in some other geometry, such as abobbin shape, cylinder or pellet to allow an alternate low surface celldesign.

The electrochemical cell of the present invention further comprises acathode of electrically conductive material that serves as the counterelectrode. The cathode is preferably of solid materials having thegeneral formula SM_(x)V₂O_(y) where SM is a metal selected from GroupsIB to VIIB and VIII of the Periodic Table of Elements, and wherein x isabout 0.30 to 2.0 and y is about 4.5 to 6.0 in the general formula. Byway of illustration, and in no way intended to be limiting, oneexemplary cathode active material comprises silver vanadium oxide havingthe general formula Ag_(x)V₂O_(y) in either its β-phase having x=0.35and y=5.8, γ-phase having x=0.74 and y=5.37, or ε-phase having x=1.0 andy=5.5, and combinations of phases thereof.

Before fabrication into an electrode for incorporation into anelectrochemical cell according to the present invention, the cathodeactive material is preferably mixed with a binder material such as apowdered fluoro-polymer, more preferably powderedpolytetrafluoroethylene or powdered polyvinylidene fluoride present atabout 1 to about 5 weight percent of the cathode mixture. Further, up toabout 10 weight percent of a conductive diluent is preferably added tothe cathode mixture to improve conductivity. Suitable materials for thispurpose include acetylene black, carbon black and/or graphite or ametallic powder such as powdered nickel, aluminum, titanium, stainlesssteel, and mixtures thereof. The preferred cathode active mixture thusincludes a powdered fluoro-polymer binder present at a quantity of atleast about 3 weight percent, a conductive diluent present at a quantityof at least about 3 weight percent and from about 80 to about 99 weightpercent of the cathode active material.

Cathode components for incorporation into the cell may be prepared byrolling, spreading or pressing the cathode active mixture onto asuitable current collector selected from the group consisting ofstainless steel, titanium, tantalum, platinum, nickel, and gold.Cathodes prepared as described above may be in the form of one or moreplates operatively associated with at least one or more plates of anodematerial, or in the form of a strip wound with a corresponding strip ofanode material in a structure similar to a “jellyroll”.

In order to prevent internal short circuit conditions, the cathode isseparated from the Group IA, IIA or IIIB anode material by a suitableseparator material. The separator is of electrically insulativematerial, and the separator material also is chemically unreactive withthe anode and cathode active materials and both chemically unreactivewith and insoluble in the electrolyte. In addition, the separatormaterial has a degree of porosity sufficient to allow flow therethroughof the electrolyte during the electrochemical reaction of the cell.Illustrative separator materials include fabrics woven fromfluoropolymeric fibers including polyvinylidine fluoride,polyethylenetetrafluoroethylene, and polyethylenechlorotrifluoroethyleneused either alone or laminated with a fluoropolymeric microporous film,non-woven glass, polypropylene, polyethylene, glass fiber materials,ceramics, a polytetrafluoroethylene membrane commercially availableunder the designation ZITEX (Chemplast Inc.), a polypropylene membranecommercially available under the designation CELGARD (Celanese PlasticCompany, Inc.), a membrane commercially available under the designationDEXIGLAS (C. H. Dexter, Div., Dexter Corp.), and a membrane commerciallyavailable under the designation TONEN.

The electrochemical cell of the present invention further includes anonaqueous, ionically conductive electrolyte serving as a medium formigration of ions between the anode and the cathode electrodes duringelectrochemical reactions of the cell. The electrochemical reaction atthe electrodes involves conversion of ions in atomic or molecular formsthat migrate from the anode to the cathode. Thus, suitable nonaqueouselectrolytes are substantially inert to the anode and cathode materials,and they exhibit those physical properties necessary for ionictransport, namely, low viscosity, low surface tension and wettability.

A suitable electrolyte has an inorganic, ionically conductive saltdissolved in a mixture of aprotic organic solvents comprising a lowviscosity solvent and a high permittivity solvent. In the case of ananode comprising lithium, preferred lithium salts include LiPF₆, LiBF₄,LiAsF₆, LiSbF₆, LiClO₄, LiO₂, LiAlCl₄, LiGaCl₄, LiC(SO₂CF₃)₃,LiN(SO₂CF₃)₂, LiSCN, LiO₃SCF₃, LiC₆F₅SO₃, LiO₂CCF₃, LiSO₆F, LiB(C₆H₅)₄,LiCF₃SO₃, and mixtures thereof.

Low viscosity solvents useful with the present invention include esters,linear and cyclic ethers and dialkyl carbonates such as tetrahydrofuran(THF), methyl acetate (MA), diglyme, trigylme, tetragylme, dimethylcarbonate (DMC), 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE),1-ethoxy,2-methoxyethane (EME), ethyl methyl carbonate, methyl propylcarbonate, ethyl propyl carbonate, diethyl carbonate, dipropylcarbonate, and mixtures thereof. High permittivity solvents includecyclic carbonates, cyclic esters and cyclic amides such as propylenecarbonate (PC), ethylene carbonate (EC), butylene carbonate,acetonitrile, dimethyl sulfoxide, dimethyl formamide, dimethylacetamide, γ-valerolactone, γ-butyrolactone (GBL),N-methyl-2-pyrrolidone (NMP), and mixtures thereof. In the presentinvention, the preferred anode is lithium metal and the preferredelectrolyte is 0.8M to 1.5M LiAsF₆ or LiPF₆ dissolved in a 50:50mixture, by volume, of propylene carbonate and 1,2-dimethoxyethane.

The preferred form of the electrochemical cell is a case-negative designwherein the anode/cathode couple is inserted into a conductive metalcasing connected to the anode current collector, as is well known tothose skilled in the art. A preferred material for the casing isstainless steel, although titanium, mild steel, nickel, nickel-platedmild steel and aluminum are also suitable. The casing header comprises ametallic lid having a sufficient number of openings to accommodate theglass-to-metal seal/terminal pin feedthrough for the cathode electrode.The anode electrode is preferably connected to the case or the lid. Anadditional opening is provided for electrolyte filling. The casingheader comprises elements having compatibility with the other componentsof the electrochemical cell and is resistant to corrosion. The cell isthereafter filled with the electrolyte solution described hereinaboveand hermetically sealed such as by close-welding a stainless steel plugover the fill hole, but not limited thereto. The cell of the presentinvention can also be constructed in a case-positive design.

An exemplary implantable medical device powered by a Li/SVO cell is acardiac defibrillator, which requires a power source for a generallymedium rate, constant resistance load component provided by circuitsperforming such functions as, for example, the heart sensing and pacingfunctions. This requires electrical current of about 1 microampere toabout 100 milliamperes. From time-to-time, the cardiac defibrillator mayrequire a generally high rate, pulse discharge load component thatoccurs, for example, during charging of a capacitor in the defibrillatorfor the purpose of delivering an electrical shock therapy to the heartto treat tachyarrhythmias, the irregular, rapid heartbeats that can befatal if left uncorrected. This requires electrical current of about 1ampere to about 4 amperes.

In order to test Li/SVO cells for their electrochemical characteristics,several accelerated discharge regimes are commonly used in the industry.One consists of discharging a Li/SVO cell under a 17.4 kΩ load withsuperimposed pulse trains applied every 60 days. The pulse trainsconsist of four 2.0 amp pulses of constant current, each of 10-secondduration with about 15 seconds rest between each pulse. One such pulsetrain is superimposed on the background load about every 2 months. Thistype of discharge is termed 1 year accelerated discharge data (1 YearADD). Table 1 lists other industry standard ADD tests and the intervalbetween each pulse train. The pulse intervals listed in Table 1 areapplicable for tests performed at 37° C.

TABLE 1 Test Type Pulse Interval  1 Year ADD 2 months  3 Year ADD 4months  5 Year ADD 6 months 36 Month ADD 3 months 60 Month ADD 5 months

One issue relative to a Li/SVO cell is the existence of voltage delayand permanent Rdc growth starting at about 35% to 70% DOD. Voltage delayand Rdc growth are believed to be associated with anode surface filmformation, which is influenced by the manner the cell is discharged.From extensive modeling studies with Li/SVO cells under the various ADDregimes, it has been discovered that the longer the ADD test time, theworse voltage delay and Rdc become. Such parameters as total dischargetime to a particular % DOD, cell current density (mA/cm²), the number ofpulses per pulse train, and the time between pulse trains, among others,are believed to affect voltage delay and Rdc growth.

In actual defibrillator device applications, one very importantparameter is the charge time to achieve a predetermined energy fortherapy delivery. In other words, the time to charge a capacitor to arequired voltage is affected by voltage delay and Rdc growth. A typicalcardiac defibrillator requires energy in the range of from about 40Joules to about 70 Joules per Li/SVO cell for electrical shock therapy.The relationship is shown below:Energy(J)=I(amp)×V(volt)×t(sec.)t(s)=Energy(J)/IV

If the required delivered energy (J) and pulsing current (amp) are bothdefined, then the charge time in seconds is inversely proportional tothe average voltage under pulsing. Therefore, to maintain a relativelylow charge time, the cell must deliver higher voltage under pulsing.This requirement is, however, compromised by the voltage delay and Rdcgrowth phenomena in the Li/SVO system at the middle of discharge liferegion (starting at about 35% DOD). Under severe conditions, cellvoltage under pulsing becomes so low that the charge time is consideredtoo long for the required therapy. This results in shortened devicelongevity. Since voltage delay and Rdc growth start at about 35% to 40%DOD, it is possible that only about 40% of the theoretical capacity of aparticular Li/SVO cell is actually delivered. The remaining capacity iswasted. Therefore, the present invention is directed to methodologiesdesigned to avoid or get around the voltage delay and Rdc growth regionin a Li/SVO cell.

A cardiac defibrillator essentially consists of an electrochemical cellas a power source for charging at least one electrolytic capacitor todeliver the electrical shock therapy to the patient's heart.Microprocessors powered by the cell perform the heart sensing and pacingfunctions and initiate capacitor charging to deliver the electricalshock therapy. Not only does the Li/SVO cell experience voltage delayand Rdc growth problems at about 35% DOD as explained above, butelectrolytic capacitors can experience degradation in their chargingefficiency after long periods of inactivity. It is believed that theanodes of electrolytic capacitors, which are typically of aluminum ortantalum, develop microfractures after extended periods of non-use.These microfractures consequently result in extended charge times andreduced breakdown voltages. Degraded charging efficiency ultimatelyrequires the Li/SVO cell to progressively expend more and more energy tocharge the capacitors for providing therapy.

To repair this degradation, microprocessors controlling the implantablemedical device are programmed to regularly charge the electrolyticcapacitors to or near a maximum-energy breakdown voltage (the voltagecorresponding to maximum energy) before discharging them internallythrough a non-therapeutic load. The capacitors can be immediatelydischarged once the maximum-energy voltage is reached or they can beheld at maximum-energy voltage for a period of time, which can be rathershort, before being discharged. These periodic charge-discharge orcharge-hold-discharge cycles for capacitor maintenance are called“reforms.” Reforming implantable defibrillator capacitors at leastpartially restores and preserves their charging efficiency.

An industry-recognized standard is to reform implantable capacitors bypulse discharging the connected electrochemical cell about once everythree months throughout the useful life of the medical device, which istypically dictated by the life of the cell. Thus, the basis for thepresent invention is driven by the desire to substantially reduce, ifnot completely eliminate, voltage delay and Rdc growth in a Li/SVO cellwhile at the same time periodically reforming the connected capacitorsto maintain them at their rated breakdown voltages. Therefore, thepresent invention relates to methodologies for significantly minimizing,if not entirely eliminating, the occurrence of voltage delay andirreversible Rdc growth in Li/SVO cells by subjecting them to noveldischarge regimes.

The first discharge methodology comprises more frequent pulses beingapplied to a Li/SVO cell than the present industry standard of aboutonce every three months deemed sufficient for capacitor reform. Thecurrent pulses can either be delivered to the device being powered bythe cell or to a secondary “dummy” circuit.

In the first methodology, the Li/SVO cell is discharged to deliver apulse train at least about once every one day to about once every 60days, more preferably once every seven days to about once every fourweeks. High current pulsing preferably consists of periodic pulse trainsof four 10-second 2 to 3 amp pulses (15 mA/cm² to 50 mA/cm²) with 15seconds rest between each pulse. At the very minimum, the cell deliversa pulse train about once every seven days to four weeks in the about 15%to about 80% DOD region, more preferably in the about 20% to about 75%DOD region, and most preferably in the about 25% to about 70% DODregion. However, it is within the purview of the present invention tosubject the cell to pulse trains of reduced interim intervals, i.e. atleast about once every seven days to about four weeks, for the cell'sremaining useful life once pulse discharge reform maintenance of theconnected capacitors begins. By significantly minimizing voltage delayand Rdc growth, especially in the 35% to 70% DOD region, the time tocharge a capacitor is well within the device application threshold. Thisallows for more practical deliverable energy.

A second methodology according to the present invention is to quicklydischarge the cell once it enters the voltage delay region. Discharge isin the form of current pulses delivered to the device being powered bythe cell or to a secondary “dummy” circuit. Such a rapid dischargeprotocol is designed to remove from about 2% to about 20% of the cell'sdischarge capacity beginning at about 15% DOD, more preferably beginningat about 20% DOD, and most preferably beginning at about 25% DOD.

A preferred protocol under the second methodology is to discharge thecell under current pulsing to remove about 10% DOD beginning at about25% DOD in a time period of from about 20 minutes to about 24-hours,then resume the normal discharge regime for capacitor reform maintenanceof about once every three months. The 2% to 20% DOD is removed from thecell by adjusting the interval between pulse trains. High currentpulsing preferably consists of periodic pulse trains of four 10-second 2to 3 amp pulses (15 mA/cm² to 50 mA/cm²) with 15 seconds rest betweeneach pulse.

In this manner, the region of severe voltage delay and Rdc growth isby-passed. In the remaining discharge region of about 45% to 80+% DOD,cell Rdc does not grow significantly, which, in turn, translates intohigher pulse voltages and shorter charge times. Therefore, at least25%+35+%=60+% of theoretical capacity is deliverable as useful energy,instead of just 35% to 40% of theoretical capacity under the traditionaldischarge regime in the worst case.

The following example describes the manner and process of anelectrochemical cell according to the present invention, and set forththe best mode contemplated by the inventors of carrying out theinvention.

EXAMPLE I

FIG. 1 is a graph drawn from the average discharge characterizationresults of two Li/SVO cell groups, each group having five cells ofsimilar construction and energy density. The cells were periodicallydischarged at 50° C. under a 16.5 kΩ load with superimposed pulse trainsapplied every 63 days. The pulse trains consisted of two 2.5 amp,10-second pulses with 15 seconds rest between each pulse. This type ofdischarge is termed 24 month accelerated discharge data (24MADD), whichsimulates 60MADD at 37° C. with pulse intervals of 154 days. The cellsused to construct curve 10 were subjected to this protocol throughoutthe entire test. However, the cells used to construct curve 12 wereswitched to a more rapid discharge protocol after the fourth pulsetrain. Then, they were pulse discharged every 14 days until the end ofthe test.

It can be seen that in the case of the cells of curve 10, the chargetime to 60 joules at pulse 1 end significantly increased after about 900mAh of capacity was removed. This corresponds to a DOD of about 35%.However, the cells of curve 12 experienced significantly less chargetime than the other cells to a similar delivered energy. The conclusionis that according to the first discharge methodology of the presentinvention, starting at about 25% DOD to about 35% DOD, voltage delay andRdc growth in a lithium/transition metal oxide cell, and particularly aLi/SVO cell, are significantly reduced by more frequently pulsedischarging the cell than the current industry standard of about onceevery three months, which is deemed satisfactory for implantablecapacitor reform.

It should be pointed out that conducting an ADD test at 50° C.accelerates discharge about 2.46 times in comparison to the same testconducted at 37° C.

It is appreciated that various modifications to the present inventiveconcepts described herein may be apparent to those of ordinary skill inthe art without departing from the spirit and scope of the presentinvention as defined by the herein appended claims.

1. A method for powering an implantable medical device with anelectrochemical cell, the cell comprising an alkali metal anode coupledto a cathode of a cathode active material activated with an electrolyte,comprising the steps of: a) connecting a negative terminal and apositive terminal of the cell to the implantable medical device; b)powering the implantable medical device with the cell; c) monitoring thedepth-of-discharge (DOD) of the cell; and d) upon the cell reachingabout 15% to about 25% DOD, discharging the cell to deliver dischargecapacity equal to at least about 2% DOD within 60 days.
 2. A method forpowering an implantable medical device with an electrochemical cell, thecell comprising an alkali metal anode coupled to a cathode of a cathodeactive material activated with an electrolyte, comprising the steps of:a) connecting a negative terminal and a positive terminal of the cell tothe implantable medical device; b) powering the implantable medicaldevice with the cell; c) monitoring the depth-of-discharge (DOD) of thecell; d) upon the cell reaching about 15% to about 25% DOD, causing thecell to deliver at least a first current pulse discharge ofsignificantly greater amplitude than that of a pre-pulse currentimmediately prior to the first current pulse discharge; e) waiting atime interval; and f) discharging the cell to deliver at least a secondcurrent pulse discharge of significantly greater amplitude than that ofa pre-pulse current immediately prior to the second current pulsedischarge after the time interval, wherein the time interval between thefirst current pulse discharge and the second current pulse discharge isfrom about 20 minutes to about 60 days.
 3. The method of claim 2including discharging the cell to deliver the first current pulsedischarge and the second current pulse discharge to the implantablemedical device or to a secondary load.
 4. The method of claim 2including discharging the cell to deliver at least two current pulsesspaced apart from about 10 to about 30 seconds as both the first currentpulse discharge and the second current pulse discharge.
 5. The method ofclaim 2 including discharging the cell to deliver about 15 mA/cm² toabout 50 mA/cm² as the first current pulse discharge and second currentpulse discharge.
 6. The method of claim 2 including discharging the cellto deliver four current pulses as both the first current pulse dischargeand the second current pulse discharge.
 7. The method of claim 2including providing the cell of a lithium/silver vanadium oxide couple.8. A method for providing electrical energy from an electrochemical cellcomprising an alkali metal anode coupled to a cathode of a cathodeactive material activated with an electrolyte, comprising the steps of:a) connecting a negative terminal and a positive terminal of the cell toa load; b) powering the load with the cell; c) upon the cell reachingabout 15% depth-of-discharge (DOD) to about 25% DOD, discharging thecell to deliver at least a first current pulse discharge ofsignificantly greater amplitude than that of a pre-pulse currentimmediately prior to the first current pulse discharge; d) waiting atime interval; and e) discharging the cell to deliver at least a secondcurrent pulse discharge of significantly greater amplitude than that ofa pre-pulse current immediately prior to the second current pulsedischarge after the time interval, wherein the time interval between thefirst current pulse discharge and the second current pulse discharge isfrom about one day to about 60 days.
 9. The method of claim 8 includingdischarging the cell to deliver the first current pulse discharge andthe second current pulse discharge to the load being powered by the cellor to a secondary load.
 10. The method of claim 8 including dischargingthe cell to deliver at least two current pulses as both the firstcurrent pulse discharge and the second current pulse discharge.
 11. Themethod of claim 8 including discharging the cell to deliver about 15mA/cm² to about 50 mA/cm² as the first current pulse discharge andsecond current pulse discharge.
 12. The method of claim 8 includingdischarging the cell to deliver four 10-second current pulses with abouta 15-second rest between each current pulse as both the first currentpulse discharge and the second current pulse discharge.
 13. The methodof claim 8 including providing the load as an implantable medicaldevice.
 14. The method of claim 8 including providing the cathode activematerial comprising silver vanadium oxide.
 15. A method for providingelectrical energy from an electrochemical cell comprising an alkalimetal anode coupled to a cathode of a cathode active material activatedwith an electrolyte, comprising the steps of: a) connecting a negativeterminal and a positive terminal of the cell to a load; b) powering theload with the cell; c) monitoring the depth-of-discharge (DOD) of thecell; and d) removing about 2% to about 20% of the cell's dischargecapacity upon the cell reaching about 15% to about 25% DOD by causingthe cell to deliver at least a first current pulse discharge ofsignificantly greater amplitude than that of a pre-pulse currentimmediately prior to the first current pulse discharge.
 16. The methodof claim 15 including discharging the cell to deliver the first currentpulse discharge to the load being powered by the cell or to a secondaryload.
 17. The method of claim 15 including discharging the cell todeliver the first current pulse discharge, waiting a time interval; andthen discharging the cell to deliver at least a second current pulsedischarge of significantly greater amplitude than that of a pre-pulsecurrent immediately prior to the second current pulse discharge afterthe time interval, wherein the time interval between the first Currentpulse discharge and the second current pulse discharge is from about 20minutes day to about 24 hours.
 18. The method of claim 15 includingdischarging the cell to deliver about 15 mA/cm² to about 50 mA/cm² asthe first current pulse discharge.
 19. The method of claim 15 includingdischarging the cell to deliver four current pulses as the first currentpulse discharge.
 20. The method of claim 15 including providing the loadas an implantable medical device.
 21. The method of claim 15 includingproviding the cathode active material comprising silver vanadium oxide.